Preparation of organoboron halides



United States Patent 0,

3,146,261 PREPARATHGN F ORGAN OBORON HALIDES Lalrrner Lynds, North Hollywood, and David R. Stern, Fullerton, Calif., assigrrors to American Potash & Chemical Corporation, a corporation of Delaware No Drawing. Filed Nov. 7, 1958, Ser. No. 772,424 1 Claim. (Cl. 260-543) This invention relates to the preparation of alkyldihaloborines and bis(dihaloborino)alkanes by a metathesis reaction between an organoboron halide and a diiferent boron trihalide, which reaction involves simple redistribution of halogens and requires no catalysts.

Organoboron compounds have recently demanded extensive investigation as starting substances for high polymers and high energy chemicals. Alkyldihaloborines and bis(dihaloborino)alkanes are important intermediates in the formation of polymers, substituted borazoles, hydrides, boronic acids and their esters and anhydrides (boroxines). They may also be used for pyrophoric fuels and it is for this purpose that they may be used directly without being converted to other compounds. A preferred utility for the alkyldihaloborines and bis(dihaloborino)alkanes is as igniters in the event of jet flameouts. These compounds also find use as preignition inhibitors in gasoline. But use of these compounds has been severely limited because of uneconomical and complicated methods of synthesis,

which in many instances gave mixtures that could not be separated into pure components.

Therefore, it is an object of this invention to provide a process for the preparation of aryl and alkyldihaloborines and bis(dihaloborino)alkanes which may be easily carried out and which provides high yields of the desired products.

A further object is to provide a method which is readily adaptable to a continuous process utilizing a flow system and inexpensive raw materials.

Broadly, it has been found that a metathetical reaction whereby halogen atoms are replaced takes place when either an aryldihaloborine, an alkyldihaloborine or a bis- (dihaloborino)alkane and a boron trihalide (the halogen of the trihalide being of greater molecular Weight than the halogen in the organo compound) are refluxed in a suitable system whereby the relatively volatile boron halide by-products can be continuously removed.

Catalysts are not necessary and in all cases the desired compounds are specifically formed. No side reactions take place to any appreciable extent, and only small quantities of mixed boron halides are detected in the by-products. Almost quantitative yields can be obtained when a stoichiometric excess of the boron trihalide is used and a suitable recovery system is employed.

A preferred reaction temperature range is from 25 C. to 180 C. though under certain circumstances even more extreme temperatures may be used with some additional inconvenience. At 180 C. most alkyldihaloborines begin to decompose and the same has been found to be the case with many of the bis(dihaloborino) alkanes. Hence, this temperature may be set as a practical upper limit for carrying out most of the process species of this invention. As a matter of convenience, the reaction temperature is customarily determined by the boiling point of the lowest-boiling component in the system. And in most instances, the boiling point of the lowest-boiling component generally falls within the range set forth above. For greatest convenience, the reactions are preferably carried out at atmospheric pressure. However, it is possible to vary pressures somewhat, although there appears to be no particular advantage in so doing.

A recovery system can easily be incorporated to recycle by-products and recover the product simultaneously, since products are always much less volatile than the by-products, making their separation an elementary problem of distillation. Yields in excess of 90% based on the boron halides may easily be realized depending on the recovery system efliciency.

The entire group of compounds containing boroncarbon bonding is highly susceptible to oxidation and, in fact, spontaneously inflammable in air, necessitating that they be handled under inert and dry atmospheres.

The general formulae representing the various metathetical reactions are set forth below.

Preparation of alkyldichloroborines:

3RBF +2BCl 3RBC15+ 2BF Preparation of alkyldibromoborines:

3RBF +2BBr 3RBBr 2BF 3RBCl '+2BBr 3RBBr +2BCl Preparation of alkyldiiodoborines:

3RBF +2BI 3RBI +2BF 3RBCl +2BI 3RBI +2BCl 3RBBr +2BI 3RBI +2BBr Reactions analogous to the above may be written for the preparation of each of the bis(dihaloborino) alkanes, of which the following is typical:

wherein R is a polymethylene group. R and R in the above reactions may also represent aralkyl groups and R and R may be cycloalkyl as well as straight or. branched chain materials. One or more of the hydrogens on the alkyl or aryl portion may also be replaced with other groups, as, for example, halogens or lower alkyl groups.

A wide variety of organo compounds will react in this manner, as set out in the following illustrative examples.

EXAMPLE I.-ETHYLDIBROMOBORINE A small quantity of boron tribromide (37.5 grams) was placed in a 250 ml. round-bottom flask and ethyldichloroborine (18.0 grams) was transferred into it on a high vacuum system. The mixture was refluxed for seven hours at the boiling point at 760 mm. Hg (SO-92 C.) until 7.6 ml. of boron trichloride was removed. This represents an yield. The product and excess boron tribromide were separated by fractional distillation under argon. Ethyldibromoborine has a boiling point of 95.0 C./ 760 mm. Hg. Analysis of the product is as follows:

Weight Percent Component Found Cale.

B 5. 2 5. 4 BL 79. 9 80. 3

EXAMPLE II.BIS (DIBROMOBORINO) ETHANE 3 mm. Hg. The distillate Was clear and colorless. Analysis of the product is as follows:

. Weight Percent may be prepared as set forth in our co-pending applica- Component tion, Serial No. 707,124, filed January 6, 1958, for Or- Fomid Oak. ganoboron Compounds.

Obviously, many modifications and variations may be B made without departing from the spirit and scope of this invention and therefore only such limitations should be imposed as are indicated in the appended claim.

Table I.-Alkyl and Aryldihaloborirzes Boron Wt. Wt. Example Dihaloborine Reaetant Trihalide Product Percent; Percent Halogen (CHmCHBClz BBra. (CHahCHBBIz 5.06 74.78 hB Q Z h. I3 I; 3, 8 91,02 CH CH(BC1g)CHzCHzBClz. B1311.-. CHaCII(BBI2)(CHz)zBBr2 5.45 80.44 CflH Boh BBram- CGI'IUBB 4.26 07.21 (CI-1m C12 Ia (0 20301312 3.49 81.90 BrCHgGH(CHa)BClz... BrCH CH (CH3)BB1-; 3, 31,92 GH3 CII2 3CH2CH1BBIZ I3 3. [)9 72. 52 CHQCH (BomoH (BC 5. so. .4 (OQHQZCHOHGBC 4.01 M23 (CHmC(BC1z)CH2CHzC(B I2)( a)2 4. 77 70. 48 f 2 (BC1z)( 2)2 2 (B CIQC fl zUH 4. 79 70.80

(31113 BIzB XIV CH3C|(BC12)CH3 BBr3.-- CH3 (B 1z)CHa 4. 51 00.07

CH3 CH3 CH3(CH 3OH(BClz)CH3 1313mm. CHawHmCIHBBmC a 2.73 40.35 CsHgCH BClfiCHzBClz BBr3 OsH OH(BBr1)OH BBrz.... 4.86 71.76 C5H5CH2GH(BG12)CH3 313m... fl 5 II2 (BBI'2) 3-- 3.73 55.14 ofimomnnmnmoni BIa cflmownntnaro a 2.82 06.09 IC H4CH(BClz)CHa- BIa 1C1; iCH(] 2)CHs.--.. 2.18 76.78 CH3C5II4CH(BC11)CI'I3 0.. 131313."- CHaCt iCH(BBT2)C 3. 73 55.14 [CH CH(BClz)(CH2)zCHBC12]1 BBla.. [C 2CH( Brz)(C z)z B r2]2 5.29 78.07

CQH5C5H-CH(CH3)(BC1B)CH3 BBls.-- CoHsCu H(C :)(BB1"2) a 2.95 43.55 1331's.-.. (CGH5)2C(BBI2)C 3.16 46. 75 BBI3 CBIISCH(BBI2)OH(BBT2)C6H5- 4.15 (11.20 BBr3 BroiihomBBrz C's 3.05 07.59 131313.... (CH3)2C(BBI2)2 5.64 83.38 B1311... (01 1930131371... 4.75 70.17 13013.... CHaBClz 11.16 73.12 B 01131312.. 3.87 90.76 CHJBFQ a BBl'3- CHBBBI'Z 5.83 86.08 C5H5C(CH3)(BF2)CH3 BC1s..-- Ct sC( a)(B 1z)C 3 5.39 35.29 (CH3);C(BF )1 13013.... (C s)2 C12)2 10. 29 69.00

Further examples are set forth in the table which fol- We claim:

lows. The formula for each haloborine reactant (and hence for the product also) is conditioned upon the assumption that the reaction by which the said reactant is prepared follows Markownikoffs rule. Hence, it is not desired to limit the invention to specific structural formulae, though there is reason to believe the structural assignments set forth here are correct.

In various of the examples set out herein, compounds of the general formula RBF are used as reactants. These A process comprising reacting in an inert atmosphere ethyldichloroborine with boron tribromide whereby to replace the chlorine bonded to the boron of said ethyldichloroborine with the bromine bonded to the boron of said boron tribrornide.

References Cited in the file of this patent McCusher et al.: J.A.C.S. 79, 5186 (1957). Martin: Boron Trifiuoride and its Derivatives (1949), page 32. 

